Polyimides were first developed in 1955 as thermoplastics. The rigid aromatic ring provides a high glass transition temperature and good mechanical strength. Polyimides have been widely used in electric and space engineering due to their excellent thermal oxidative stability, chemical resistance, and low dielectric constant. Most thermoplastic aromatic polyimides in the fully imidized state are insoluble and infusible. Thus, polyimides are typically processed in the form of poly (amic acid) (PAA) precursors. After casting, the films or coatings are imidized state at evaluated temperature (˜300° C.). The high processing temperature limits polyimide usage. Another problem with this process is that the PAA solution is sensitive to humidity, which may result in the chain scission during the storage period. In addition, the water released from the imidization process may cause voids in the products, especially when processing relatively high molecular weight polymers to produce thick films or composites. More recently, the thermoplastic polyimides have been developed with good solubility in common solvents, however a drawback of the soluble polyimides is the poor chemical resistance.
To ameliorate some of the processing issues with thermoplastic polyimides, thermosetting polyimides were developed by NASA in early 1960s. Thermosetting polyimides are usually low molecular oligomers with reactive functional groups on the backbone or side chain which crosslink upon heating. The reactive functional groups, such as nadimide, maleimide and acetylene, can undergo homo or copolymerization upon heating.
The high cross-linking temperature of polyamides is barrier that prevents there use beyond their current niche applications. Presently, there is a need in the art for polyimides and methods of curing polyamides at lower temperatures.